Magnet-switch.



T. VARNEY.

MAGNET SWITCH.

APPLICATION man AUG. 12. 1912.

Patented Nov 13, 1917.

ATTORNEY UNITED STATES PATENT OFFICE.

THEODORE VARNEY, 0F PITTSBURGH. PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

MAGNET-SWITCH.

Specification of Letters Patent.

Patented Nov. 13, 1917.

To all whom it may concern:

Be it known that I, THEODORE VARNEY, a citizen of the United States, and a resident of Pittsbur h, in the county of Allegheny and State 0 Pennsylvania, have invented a new and useful Improvement in Magnet- Switches, of which the following is a. specification.

My invention relates to electric circuit switching devices, and it has special reference to such devices as are operated by electromagnets and are known as magnet switches.

The object of my invention is to provide a relatively simple device of the class above indicated that shall be particularly adapted for use in systems of electric motor control embodying a plurality of mechanically independent switches and that shall be characterized by the property of closing only when the value of the current supplied to its magnet coil falls within predetermined limits.

Switching devices having the general opcratingcharacteristics above specified have hitherto been utilized and are now well known. The switch. of my invention, however, difi'ers from those of the prior art in several essential particulars. The electromagnetic pull upon an armature having the movablecontact member is always suflicient to close the switch when the magnet is energized', mechanical devices being relied upon for holding the switch open when the current supplied to its actuating magnet exceeds a predetermined value. I

Figure 1 of the accompanying drawings is an elevation of a switch constructed in accordance with my invention. Fig. 2 isa simple diagram illustrating the circuit connections for a motor-control system embodyin several of the switches shown in Fig. 1.

Tieferring to Fig. 1 of the drawings, the switch here shown comprises an insulating base or face plate 1, a stationary contact member 2 which is secured thereto by a bolt 3 and a nuts, an electromagnet comprising a stationary core member 5 secured to the face plate 1 by bolts 6 and nuts 7, a coil 8, an armature 9, a movable contact member 10 which is secured to the armature 9, and an' escapement latching mechanism 11.

The stationary core member 5 is of sub stantially U-shape, the coil 8 being mounted pivotally connected to the outer end of its lower arm.

The movable contact member 10 is pivotally connected to the outer end of the armature 9 and is provided with a spring 12 which tends to produce a rotative movement of the contact member in a counter-clockwise direction. The member is limited in its movement, however, by stop projections 13, the arrangement of parts being such that a wiping contact is produced between the members 2 and 10 when they come into engagement with each other.

The escapement latch mechanism 11 comprises a member 14 of U-shape which is supported by av stationary bracket 16, and a pair of latches 19 and 20 which are pivotally connected to the outer ends of the arms of the member 14.

The member 14 is connected to the bracket 16 by a pair of links 21 and "2:2., and is supported directly below the core member 5 of the electromagnet on a projection 15 of the bracket. The upper arm. of the member 14: is constructed of magnetizable material and constitutes an auxiliary armature 14 of the magnet 5-8. The latch 19 is-provided with a spring 25 which tends to move its lower .end outwardly, but such movement is limited by stop projections 26.

The latch 20 is provided with a spring 27 which tends to move its upper end outwardly but such movement is limited by cooperating stop'projections 28.

The armature 9 is provided with an arm 29, preferably of non-magnetizable material, which extends to a point substantially midway between the arms of the member 14 when" the switch occupies its open position. The arm 29 is provided with a pin 30 which projects laterally therefrom and engages the one or the other of the latches 19- and 20 under predetermined conditions.

Assuming that the parts occupy the positions indicated in Fig. 1 of the drawings, if current is supplied to the coil 8 in excess of a predetermined value, the armature 9 will be attracted toward the upper arm of the core member 5 but will be held in its open circuit position by the engagement of the pin 30 with the latch. 19.

As hereinafter explained, the leakage flux from the lower arm of the core member 5 will traverse the auxiliary armature 14 and will raise the member 14 and thus move the latch 19 out of range of the pin 30. The switch will consequently be permitted to move toward its closed position until the pin 30 engages the latch 20.

The switch parts will then remain at rest until the current in the coil 8 and the flux in the lower arm of the magnet 5 are sufficiently reduced to permit the member 14 to fall. This downward movement of the member 14 carries the latch 20 out of range of the pin 30, and, since the latches 19 and 20 are oifset relative to each other, the armature will'be released and the switch will be permitted to close.

I prefer to employ a short circuited turn or coil 31 of conducting material on the lower arm of the member 5 in order to insure that the member 14 will be raised when current is first supplied to the coil 8. The lower arm of the core member may, however, be sufficiently reduced in cross sectional area to allow it to become saturated when the current exceeds a predetermined value thereby materially increasing the leakage flux at and above the aforesaid predetermined value and producing the desired movement of the member 14.

The auxiliary armature 14 is provided with polar projections 50 which are preferably capped with non-magnetizable spacers 51 to prevent the armature from sticking to the adjacent arm of the core member 5.

It will be understood by those skilled in the art that such independently operated switches as are employed for controlling the acceleration of the electric motors are usually supplied with abnormally large currents when a motor is first connected to its supply circuit or when a section of the accelerating resistance is excluded.

Referring to Fig. 2 of the drawings, the system here shown comprises an electric m0- tor having an armature 32 and a field magnet winding 33, a line switch 3.4, resistor sections 35, 36 and 37, accelerating switches 38, 39 and 40, and a master switch 41.

Assuming that each of the switches 38, 39 and 40 corresponds structurally to the switch shown in Fig. 1, if master switch 41 is closed,'ener y is first supplied from a line conductor 42 through the switch 41, a coil 43 of the switch 34, and a conductor 44 to an opposite line conductor 45.

The switch 34 is thus closed and a motor circuit is established from the conductor 42 through the armature 32, the field magnet winding 33, the switch 34, a coil 46 of the switch 38, resistor sections 35, 36 and 37, and the conductor 44 to the opposite line conductor.

The motor circuit is thus established, with the resistor sections and the coil 46 of the switch 38 included in series relation.

The switch 38 is not closed immediately, however, by reason of the characteristics hereinbefore described. After the current traversing its coil falls below a predetermined value, it will close and will complete the motor circuit from the switch 34 through the coil 46, the switch 38, a coil 47 of the switch 39, resistor sections 36 and 37 and conductor 44 to the opposite line conductor.

The switch 39, when closed, completes the motor circuit through the switch coils 46 and 47, a coil 48 of the switch 40, resistor section 37 and conductor 44 to the opposite line conductor, and, when the switch 40 is closed, the motor circuit is completed directly from the line switch 34 through the coils 46, 47 and 48 of the accelerating switches, the resistor sections being short circuited.

The arrangement whereby a latching mechanism is employed to delay the closure of the switch possesses a number of advantages over the devices of the prior art. The switch is held open by the latching device which positively prevents its operation except under predetermined conditions. It has been found that the operation of switches heldopen by electromagnetic means only is more or less uncertain. The amount of energy required in actuating the latching mechanism is very small compared with that necessary to hold the switch open directly by shunt flux of the magnet. In this regard, it may be stated that it is well known that a' latch may be released by a small amount of energy although it is capable of resisting a considerable force.

My invention is, of course, not restricted to the specific details illustrated in Fig. 1, nor is it confined to any particular class of service, and 'lfdesire that only such limitations shall "be imposed as are indicated in the appended claims.

1 claim as my invention:

1. The combination with a switch comprising a movable member and an electromagnet for controlling said member, of means for preventing the closing of said switch except after a predetermined sequence of changes in the energization of said electromagnet, said means comprising a plurality of elements to be successively engaged by said movable member.

2. The combination with a switch comprising a movable member and an electromagnet for controlling said member, of means for preventing the closing of said switch except after predetermined changes in the value of the current traversing the coil of said electromagnet, said means comprising a plurality of stop members to be successively engaged by said movable member during its closing movement.

3. The combination with a switch comprising a movable member and an electromagnet for controlling said member, of

means for preventing the closing of said switch under predetermined conditions, said means compr'sing an armature member actuated by lealiage flux of said electromagnet, and a plurality of stop members interposed in the path of movement of said-movable member, said stop members being arranged for successive engagement by said movable member.

4. The combination With a switch comprising a movable member and an electromagnet for controlling said" member, of means for preventing the closing of said switch under predetermined conditions, said means comprising an armature member actuated by leakage flux of said electromagnet, and a plurality of stop members connected to said armature member that are successively engaged by said movable member in magnet for controlling said member, of

means for preventing the closing of said switch under predetermined conditions, said means comprising an armature member controlled by leakage flux of said electromagnet and means for successively engaging said movable member upon the reciprocation of said armature member.

In testimony whereof, I have hereunto subscribed my name this 31st day of July,

THEODORE VARNEY. \Vitnesses:

F. D. HALLOCK, B. B. HINES. 

